� Perspective
&� *FAST* Texture mapping in BASIC!
 � By Philip Mellor (aged 15)
(� Acorn User/Star Info
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�15:�13:�
F?st=4:� 4 for Arm 3 or better, 8 for Arm 250s, 12 for Arm 2s
P:
Z� � �3:�:�" - ";�:�
d:
ndir$="Sprite"
xfile%=�(dir$)
�size%=�#file%+64
��#file%
�� sprite% size%
�sprite%!0=size%
�"ș "OS_SpriteOp",256+9,sprite%
�(ș "OS_SpriteOp",256+10,sprite%,dir$
�:
�� ScaleFactors 20
�:
�s$="picture"
�:
�wave1=�(1):wave2=�(1):fr=1
�ȗ � 192,420

:

�

ș6,112,fr:�

"ȗ X,Y,Z

,(top=�(�(wave1)*280)+720:wave1+=0.066

6'bot=�(�(wave2)*280)+720:wave2+=0.09

@� X>1279-892 X=1279-892

J� Y>1023-148 Y=1023-148

T$�wave(s$,X,Y,892,148,top,bot,st)

^ș6,113,fr:fr=3-fr:Ȗ

h�0

r:

|$� �wave(s$,awx,awy,w,h,s1,s2,st)

�� size,o

�size=s2:step=(s2-s1)/(h/st)

�o=0

�� ty=awy � awy+h � st

�o=(w-size)/2

��24,0;ty;1279;ty+st;

��VDU24,awx;ty;awx+w;ty+st;

�&�scale(s$,awx+o,awy,size,size,w,w)

�size-=step

��

��

�:

�!� �scale(sn$,x,y,x1,y1,x2,y2)
#� x1=0 � y1=0 � x2=0 � y2=0 � �
)!ScaleFactors=x1:!(ScaleFactors+4)=y1
.!(ScaleFactors+8)=x2:!(ScaleFactors+12)=y2
&5ș&0000002E,52+256,sprite%,sn$,x,y,0,ScaleFactors
0�
�

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00000020  78 74 75 72 65 20 6d 61  70 70 69 6e 67 20 69 6e  |xture mapping in|
00000030  20 42 41 53 49 43 21 0d  00 1e 20 f4 20 42 79 20  | BASIC!... . By |
00000040  50 68 69 6c 69 70 20 4d  65 6c 6c 6f 72 20 28 61  |Philip Mellor (a|
00000050  67 65 64 20 31 35 29 0d  00 28 1a f4 20 41 63 6f  |ged 15)..(.. Aco|
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00000090  66 6f 72 20 41 72 6d 20  33 20 6f 72 20 62 65 74  |for Arm 3 or bet|
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000001a0  63 61 6c 65 46 61 63 74  6f 72 73 20 32 30 0d 00  |caleFactors 20..|
000001b0  d2 05 3a 0d 00 dc 10 73  24 3d 22 70 69 63 74 75  |..:....s$="pictu|
000001c0  72 65 22 0d 00 e6 05 3a  0d 00 f0 1e 77 61 76 65  |re"....:....wave|
000001d0  31 3d b3 28 31 29 3a 77  61 76 65 32 3d b3 28 31  |1=.(1):wave2=.(1|
000001e0  29 3a 66 72 3d 31 0d 00  fa 10 c8 97 20 b8 20 31  |):fr=1...... . 1|
000001f0  39 32 2c 34 32 30 0d 01  04 05 3a 0d 01 0e 05 f5  |92,420....:.....|
00000200  0d 01 18 10 c8 99 36 2c  31 31 32 2c 66 72 3a db  |......6,112,fr:.|
00000210  0d 01 22 0c c8 97 20 58  2c 59 2c 5a 0d 01 2c 28  |.."... X,Y,Z..,(|
00000220  74 6f 70 3d a8 28 b5 28  77 61 76 65 31 29 2a 32  |top=.(.(wave1)*2|
00000230  38 30 29 2b 37 32 30 3a  77 61 76 65 31 2b 3d 30  |80)+720:wave1+=0|
00000240  2e 30 36 36 0d 01 36 27  62 6f 74 3d a8 28 b5 28  |.066..6'bot=.(.(|
00000250  77 61 76 65 32 29 2a 32  38 30 29 2b 37 32 30 3a  |wave2)*280)+720:|
00000260  77 61 76 65 32 2b 3d 30  2e 30 39 0d 01 40 1b e7  |wave2+=0.09..@..|
00000270  20 58 3e 31 32 37 39 2d  38 39 32 20 58 3d 31 32  | X>1279-892 X=12|
00000280  37 39 2d 38 39 32 0d 01  4a 1b e7 20 59 3e 31 30  |79-892..J.. Y>10|
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000002d0  2c 66 72 3a 66 72 3d 33  2d 66 72 3a c8 96 0d 01  |,fr:fr=3-fr:....|
000002e0  68 06 fd 30 0d 01 72 05  3a 0d 01 7c 24 dd 20 f2  |h..0..r.:..|$. .|
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00000300  77 2c 68 2c 73 31 2c 73  32 2c 73 74 29 0d 01 86  |w,h,s1,s2,st)...|
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00000330  29 2f 28 68 2f 73 74 29  0d 01 9a 07 6f 3d 30 0d  |)/(h/st)....o=0.|
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00000350  79 2b 68 20 88 20 73 74  0d 01 ae 10 6f 3d 28 77  |y+h . st....o=(w|
00000360  2d 73 69 7a 65 29 2f 32  0d 01 b8 18 ef 32 34 2c  |-size)/2.....24,|
00000370  30 3b 74 79 3b 31 32 37  39 3b 74 79 2b 73 74 3b  |0;ty;1279;ty+st;|
00000380  0d 01 c2 1e f4 56 44 55  32 34 2c 61 77 78 3b 74  |.....VDU24,awx;t|
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000003a0  cc 26 f2 73 63 61 6c 65  28 73 24 2c 61 77 78 2b  |.&.scale(s$,awx+|
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000003c0  77 2c 77 29 0d 01 d6 0e  73 69 7a 65 2d 3d 73 74  |w,w)....size-=st|
000003d0  65 70 0d 01 e0 05 ed 0d  01 ea 05 e1 0d 01 f4 05  |ep..............|
000003e0  3a 0d 01 fe 21 dd 20 f2  73 63 61 6c 65 28 73 6e  |:...!. .scale(sn|
000003f0  24 2c 78 2c 79 2c 78 31  2c 79 31 2c 78 32 2c 79  |$,x,y,x1,y1,x2,y|
00000400  32 29 0d 02 08 23 e7 20  78 31 3d 30 20 84 20 79  |2)...#. x1=0 . y|
00000410  31 3d 30 20 84 20 78 32  3d 30 20 84 20 79 32 3d  |1=0 . x2=0 . y2=|
00000420  30 20 8c 20 e1 0d 02 12  29 21 53 63 61 6c 65 46  |0 . ....)!ScaleF|
00000430  61 63 74 6f 72 73 3d 78  31 3a 21 28 53 63 61 6c  |actors=x1:!(Scal|
00000440  65 46 61 63 74 6f 72 73  2b 34 29 3d 79 31 0d 02  |eFactors+4)=y1..|
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00000460  2b 38 29 3d 78 32 3a 21  28 53 63 61 6c 65 46 61  |+8)=x2:!(ScaleFa|
00000470  63 74 6f 72 73 2b 31 32  29 3d 79 32 0d 02 26 35  |ctors+12)=y2..&5|
00000480  c8 99 26 30 30 30 30 30  30 32 45 2c 35 32 2b 32  |..&0000002E,52+2|
00000490  35 36 2c 73 70 72 69 74  65 25 2c 73 6e 24 2c 78  |56,sprite%,sn$,x|
000004a0  2c 79 2c 30 2c 53 63 61  6c 65 46 61 63 74 6f 72  |,y,0,ScaleFactor|
000004b0  73 0d 02 30 05 e1 0d ff                           |s..0....|
000004b8